Senior Hamas officials say Haniyeh's hospitalization was a result of his living underground for so long, but others say Hamas political leader Khaled Mashaal, furious at Haniyeh for accepting the Egyptian cease-fire proposal, wanted him removed.

Rumors spread in the Gaza Strip on Thursday that Hamas leader Ismail Haniyeh had been poisoned after he was hospitalized on Wednesday night with "chest pain" shortly after finishing his speech declaring Hamas' victory in the last round of fighting with Israel.

Hamas initially tried to hide Haniyeh's medical condition, but after rumors spread that he had been hospitalized the group released a statement saying that Haniyeh, the former Hamas prime minister who is likely to become the group's next political leader, "has been taken to Shifa Hospital, where he underwent a series of tests and was admitted for observation."

Senior Hamas officials claimed that Haniyeh's long stay underground during the fighting and his limited exposure to fresh air and light, as well as poor nutrition, took a toll on his health.

But the Hamas leader's continued absence led many to believe his sickness was not a coincidence.

One theory is that Haniyeh was poisoned. Some accused Israel of poisoning him, but others blamed Qatar-based Hamas political leader Khaled Mashaal, saying he was furious over the fact that Haniyeh had agreed to the Egyptian cease-fire proposal, and has decided to get rid of Haniyeh.

Mashaal has denied reports of tensions between him and Haniyeh, who along with senior Hamas official Moussa Abu Marzouk, circumvented the Hamas chief and accepted Cairo's truce proposal. In a clear showing of his discontent, when reading out all the groups he thanked for aiding Hamas during the fighting, Mashaal named almost everyone possible -- except the Hamas leadership in Gaza.